1. Field of the Invention
This invention relates to apparatus and methods for chemical vapor deposition of thin films on silicon wafers. More particularly, this invention relates to apparatus and methods for heating semiconductor wafers by creating a predetermined temperature profile across a support platen by means of multiple heaters.
2. Description of the Prior Art
In chemical vapor deposition systems, it is important to have complete control of heating the semiconductor wafer substrate. Sometimes it is necessary to heat the substrate uniformly. Non-uniform heating at these times can result in non-uniform deposition. At other times it is desirable to create a non-uniform temperature profile across the wafer in one direction while maintaining a uniform temperature profile in another direction. Chemical vapor deposition heating systems of the prior art, such as heat lamp or induction systems, have difficulty maintaining a desired heat profile across the wafers. These systems heat the wafer satisfactorily, but the difficulty occurs from their lack of control.
Since the chamber in which low pressure chemical vapor deposition occurs is evacuated during the operation, it is important that the voltage applied to the heater be kept low so as to prevent arcing across the terminals. There is a trade off of sufficient voltage to provide enough power to heat the wafer but not so much voltage as to initiate arcing across the heater terminals.
Accordingly, it would be desirable to have a platen heater for a chemical vapor deposition system that is capable of providing a desired temperature profile or gradient across a support platen. Furthermore it would be desirable to have a platen heater for a chemical vapor deposition system that has low cost and high efficiency. Furthermore, it would be desirable to have this platen heater operate at sufficiently low voltage as to inhibit arcing at the terminals or elsewhere (enhances personnel safety also). These benefits and others will become apparent as the platen heater system is described according to the teachings of the invention.